1. Field of the Invention
Embodiments of the present invention generally relate to control of solid state lasers. More particularly, embodiments of the present invention relate to methods for shutting down solid state lasers during abnormal events.
2. Description of the Related Art
Solid state lasers have many applications in a variety of fields. For example, solid state lasers may be used during substrate processing for manufacture of integrated circuit devices, thin-film-transistor devices, flexible substrate applications, organic light emitting diodes, and solar cell devices. One application of solid state lasers is for rapid thermal annealing of a substrate during the manufacturing process of various devices.
FIG. 1 illustrates a schematic diagram of a laser based annealing system for substrate processing. The laser based substrate annealing system includes a system controller 10, a laser power supply 12, a laser 13 including the laser housing body and components within the housing body necessary to create a laser beam 14, and a hardware protection system 16. The laser based annealing system may be used to anneal a substrate 15 or portions thereof using a laser beam 14. The system controller 10 generates a control signal 17 to set the output current or power of the laser power supply 12 with laser current control signal 9. By changing the operating current or power for laser 13, the controller sets the energy of the laser beam 14, and therefore the annealing temperature of the substrate 15.
If during wafer processing a system malfunction occurs, a hardware protection system 16 turns off the laser power supply 12 by changing the status of interlock signal 18 from ON to OFF. Removing interlock signal 18 from laser power supply 12 abruptly sets the laser current signal 9, and thus the laser power, to zero. Since the laser temperature depends on the output power of the laser power supply, the temperature of the laser also changes from an operation level to an idle level. Fast temperature changes may create thermal stresses in the laser, which are known to cause structure defects inside the laser housing body.
Lasers can also be damaged if the laser controller malfunctions. A malfunction of system controller 10 may abruptly turn off the laser power supply 12. Hence, this type of event may also create thermal stresses in the laser housing body.
Other fields may also use solid state lasers during manufacturing or other processes, such as repair and testing. While using solid state lasers, such as high power solid state lasers, during such processes, unplanned and abnormal events may occur with the processing system, causing the laser controllers to stop functioning and prematurely shutting down. Instantaneous shut down of the solid state lasers may cause thermal stresses on laser components, resulting in internal defects that may lead to reduced efficiency or inoperability of the laser. Accumulation of these internal defects prior to inoperability degrades the laser efficiency and requires revision of process recipes.
Therefore, there is a need to improve control of power variation of solid state lasers during unplanned and abnormal events to reduce and/or prevent thermal stresses on laser components, resulting in internal defects that may lead to reduced laser efficiency and inoperability.